Once again, its mostly a question of operator precedence and how generous we are with parentheses. You are right. Im always working in assembler when I really get deep into debugging. Note that the sizeof operator is one exception that doesnt follow pointer arithmetic rules, but only deals in bytes. No, that's exactly the right way to do it. As suggested above, on my system, my complier has 64 bit pointers but size_t and ptrdiff_t are 32 bits. If youve put in a couple of years of assembly, C is clear, simple and you are greatfull for that. Another important point to note is that when we increment and decrement pointer variable by adding or subtracting numbers then it is not . Notice that at the end of the file are a bunch of one-line declarations of various types that appears to be how less-stable declarations are being written. But I expect to get back to Java soon. one that uses 1 byte addressing, btw, very unlikely), then it will be doable, and only then would it be safe to do so. Dont teach this to newbies, it is plain dangerous code, especially in the gcc era we live in. This issue is on any Real Mode processors. There is a reason of sorts for this, but ultimately these kinds of rules are just stupid. It simply has to do with the fact that pointers, in 64bit addressing, require 8 bytes of space, thus the successive printf statements below will always show an increment of 8 bytes between the 1st and 2nd calls: Thanks for contributing an answer to Stack Overflow! And theoretically it would benefit the process of learning C, if you were read it. When a pointer is decremented, it actually decrements by the number equal to the size of the data type for which it is a pointer. p1=p2+2; &so on. Even trivial program like beep are infested with grave security bugs that languish for decades before any of those many eyes ever bothers to look. Keep in mind that we dont have any allocated memory beyond values size, so we shouldnt dereference cptr1. My comment was on the valid, No, I think you are on the right track, just some of the rational is off a bit. Both operators are supported in two forms: postfix ( p++ and p--) and prefix ( ++p and --p ). The result of the sizeof operator is type size_t which is printed with %zu not %ld. NULL is 0, which is the null pointer constant, but the null pointer isnt necessarily 0. The sizeof operator will output its size accordingly, for example 8 bytes. What do you want to make/do? It returns true for the valid condition and returns false for the unsatisfied condition. That is to say, Ive never encountered a problem where the only tenable solution was to do something clever with pointer arithmetic. (Comment Policy). It depends. If you think that the pointer construct is supported by any assembly language, you dont truly understand the basic concept of assembly language, or assembly-language programming. It is only a coders convention rule to use NULL to represent an invalid address. C allows that unless, If the resulting pointer is not correctly aligned for the referenced type, the behavior is undefined. By using our site, you How to check for #1 being either `d` or `h` with latex3? This is a C vs C++ difference. Actually there are implementations where a pointer has a size of 1 byte. C++ Pointer Arithmetic. NUL, not to be confused with the NULL pointer, is simply ASCII character 0x00 or '\0'. You really don't want to do thator, perhaps, why on earth do you think you want to do that (because you really don't want to do that!)? If you want to sneak subtle bugs into a codebase, leaving out the parentheses and testing the readers attention to operator precedence is a good bet. Suppose an integer pointer int * ptr. It no longer points to a pointer of any type, and dereferencing it is therefore undefined behavior. Clearly if Im using the C language, then the C language is Just and Wise. Pointers are good, powerful, and whether you like them or not, used extensively in every object oriented language, even those that hide them from you. Just remembering that everthing is RPN is usually enough to clear my mind. Then came then came the rest of the languages. a) its strange to see it that way so you pay more attention to the expected value I dont see any comipler will catch this as an eror. Below is the implementation to illustrate the Subtraction of Two Pointers: Pointer Arithmetic on Arrays:Pointers contain addresses. There is a course much later, perhaps for graduate students that tries to teach them C. I am told that many students have big problems with it. Lots of microntrollers use it and its a nice step up from assembly language. Hence, there are only a few operations that are allowed to perform on Pointers in C language. The Modern WWW, Or: Where Do We Want To Go From Here? What language are embedded RTOS written in? So if it compiles to the same code, but there is a difference is the likelihood of mistakes, then that is an easy decision. Both printf examples invoke undefined behavior. I strongly disagree. It just seems so much more likely that you wrote the word humans instead of me. Or that you have an impossibly-small value of chock-full, perhaps even so small as to be equal to the mean of bugs in software generally. Are we saying the same thing ? Ill tell you what the CS department at the university here is/was teaching. My current solution is. Which of the following arithmetic operations is allowed on pointer variables? As a fun exercise of premature micro optimization I'm looking of a way to increment uint32 stored as [4]byte with same performance as regular ++ increment. . With a few exceptions: we can always cast to/from void* and we can always cast from pointer-to-type to char*. Im not sure if they still work this way with true VM I havent programmed on a Mac since the early 90s.